Guarantee a node-style async function is only executed once.
var once = ;var count = 0;var myAsyncFunc =;;;;
Takes a node-style async function (
fn) to ensure it's only called once. The function should accept a callback as its last parameter which is called with
cb(err, result). Returns a function that can be called any number of times but will only execute once. Arguments passed to the returned function will be passed to the